http://www.womanmagazine.co.uk/wp-content/uploads/2012/02/STACK-SPRING2012.jpg This is a stack of pictures.. On top of the stack is a picture of a family riding bicycles. At the top of the picture I see the sky. At the bottom of the picture I see the wheels of the bicycle. Underneath the picture are more pictures in the stack. Underneath the stack are pictures of a cat, a family camping, a mother and baby, and a child blowing bubbles.

Yes the first two examples you are speaking of the pictures position. In the last two examples you are speaking of a position inside the picture.